In recent years, from the perspective of vehicle safety, improvement in safety of tires on wet road surfaces has been demanded. Moreover, from the perspective of reduction of carbon dioxide emissions along with a growing interest in environmental issues, further fuel efficiency of vehicles has also been demanded.
For these demands, conventionally, as a technique for simultaneously pursuing improvement in performance of tires on wet road surfaces and reduction in rolling resistance, a method of using an inorganic filler such as silica as a filler of a rubber composition for use in tire treads has been known to be effective. However, a rubber composition comprising an inorganic filler such as silica, which has a high viscosity in unvulcanized state and requires multistage kneading, while reducing the rolling resistance of tires, improving the braking property on wet road surfaces, and improving driving stability, has a problem in workability. Therefore, in the rubber composition comprising an inorganic filler such as silica, breaking strength and wear resistance significantly deteriorate, and problems such as delayed vulcanization and poor dispersion of fillers occur. Thus, when an inorganic filler such as silica is compounded in a rubber composition for treads, it is essential to add a silane coupling agent so as to decrease the viscosity in the unvulcanized state of the rubber composition, ensure the modulus and the wear resistance, and also further decrease the hysteresis loss.